1. Field of the Invention
The present invention relates to an earphone, and more particularly, to an earphone structure with a composite sound field.
2. Description of the Related Art
Along with the progress of the digital technology, people's entertainment also becomes digitalized. For example, the digital video disc (DVD) player is a commonly used video playing apparatus in family life nowadays. Since the DVD player basically supports Dolby Digital or Digital Theater System (DTS) decoding functions, it can decode the digital signal and provide the analog signal to speakers for sounding.
In order to have a high quality digital AV entertainment life, a multi-channel speaker is a mandatory device, and the 5.1 channel speakers are a base of the multi-channel speaker.
FIG. 1 is a schematic diagram of a home theater with 5.1 channel speakers. Referring to FIG. 1, when a DVD player 100 is playing an AV title, different sound signals are respectively provided to a left speaker 102a of the front main channel, a right speaker 102b of the front main channel, a center speaker 104, a left speaker 106a of the surround channel, a right speaker 106b of the surround channel, and a subwoofer speaker 108, so as to generate a 3D sound effect and to provide an environment for simulating a real theater effect.
However, an earphone is required for listening audio when it is not suitable to use the speaker (e.g. to prevent from disturbing others). Referring to FIG. 2A, since a general earphone 200a only has one speaker 210 at its left and right side portion respectively, it is not possible for a user to enjoy the multi-channel sound effect provided by the DVD player.
Therefore, an earphone with more speakers as shown in FIG. 2B is disclosed in the prior art. The earphone 200b comprises a front main speaker 202, a center speaker 204, and a surround speaker 206 at both sides of the earphone 200b. A special design plug 208 is also provided, such that the DVD player can provide the audio signal of different channel to different speaker via the plug 208 to generate the home theater sound effect by the 5.1 channel speakers as shown in FIG. 1. However, the conventional earphone 200b uses a digital design (e.g. digital circuit design) to control a delay time of the output audio signal, thus the sound field is rather poor. Comparing to the home theater sound effect of the 5.1 channel speakers as shown in FIG. 1, its sound effect is far behind and is too poor to express the quality and effect of the multi-channel surround sound.
An earphone with a plurality of internal speakers as shown in FIGS. 2C, 2D, and 2E is further disclosed in the prior art. It is a new invention for improving the earphone structure disclosed in ROC patent no. 534566. As shown in FIGS. 2C, 2D, and 2E, each of the channel speakers 21, 22, 23, and 24 inside the case 10 is isolated respectively by its individual room 11, 12, 13, and 15, so as to have its independent sound field. The independent sound field can prevent the sound generated by each of the channel speakers 21, 22, 23, and 24 from mixing up with the sound generated by other channel speakers. In addition, each of the channel speakers 21, 22, 23, and 24 can express the characteristic of its individual speaker via different angles. However, the conventional earphone structure in which each channel speaker having its individual room has its physical disadvantage. For example, since the sound generated by each channel speaker is limited in the individual room first, and then directly propagated to user's ear, a can-tone effect is generated accordingly. In other word, a noise similar to a tone propagated via a can is generated. The more of the channel speakers and their individual rooms, the more serious the can-tone effect. As a result, the quality of the multi-channel surround effect is undesirable, and the efficiency is not acceptable.